This dish can be made Kosher for Passover, by using lamb shoulder instead of the leg.
With a whisk, blend all the ingredients (except the lamb) until emulsified. Place the lamb in a brining bag, large Ziplock, or some other large air tight container. Pour the marinade over the lamb, and seal. Refrigerate over night. Preheat oven to 450 degrees. Roast the lamb at 450 for 20 minutes, then reduce the heat to 400 degrees. Continue to cook for about an hour (about 12 minutes a pound for medium). Let the meat rest for 10 minutes before carving.